Cardiovascular and Interventional Radiological Society of Europe
Science for people
Science for people
Science for people
ProgrammeTopic highlightsFusion imaging, navigation, and planning

Fusion imaging, navigation, and planning

We caught up with Dr. Reto Bale to get a preview of his lecture on fusion imaging, navigation, and planning.

Catch the corresponding lecture in the Advanced technology in IO session.

Interventional oncology must become reliable and reproducible. Especially in tumours greater than 2-3 centimetres, complete in sano ablation from a single-probe position may not be possible despite the use of the latest MWA technology. In such cases, multiple overlapping ablation zones are required which can only be achieved by precise placement of multiple needles or by multiple needle repositionings. These tasks are difficult to achieve under conventional US-/CT-guidance. Technical solutions for 3D- planning, image guidance, and image fusion already exist.


The percutaneous stereotactic ablation workflow our team developed includes all these features, and it may be used in combination with any available ablation technology. Since our first stereotactic radiofrequency ablation (SRFA) in 2001 [1], followed by the first stereotactic microwave ablation (SMWA) in 2008, the first stereotactic irreversible electroporation (SIRE) in 2013, and the first stereotactic cryo ablation in 2014, we successfully treated > 4,000 primary and secondary liver tumours in > 1,000 patients with percutaneous stereotactic thermal ablation (mainly SRFA).


The stereotactic approach allows for precise three-dimensional planning and placement of multiple needles/probes in order to achieve overlapping ablation zones to cover large tumours.


Image fusion should be mandatory for every ablation procedure


Image fusion [2] is an integral part of the workflow and allows for immediate intraprocedural verification of the safety margin, which is an independent predictor of treatment success. Image fusion software is used to superimpose the intraoperative contrast-enhanced control CT to the planning CT for verification of complete coverage of the tumour by the ablation zone. It enables the interventional radiologist to see the results of stereotactic thermal ablation before the patient even wakes up. This intraoperative verification is a key advantage as compared to radiation therapy, which requires waiting until long-term follow-up imaging has been completed.


Image fusion is integrated into our stereotactic neuronavigation system and has been used since our very first SRFA in 2001. However, if a stereotactic system is not available, one should at least use a stand-alone image fusion software during every conventional CT-guided percutaneous ablation.


Thermal ablation of CT ‘invisible’ liver tumours using MRI fusion


In a recent study [3], 60 patients with 199 lesions not visible in CT underwent SRFA using MRI-fusion and were compared to a matched control group without image fusion. In the fusion group, major complications occurred in 8.7%. The LR rate was 3.5% in HCCs and 4% in metastases. The LR rate of metastases in the control group was significantly higher, although differences in OS and DFS did not reach statistical significance.


Histopathological results after SRFA


In a recent study [4] published in Hepatology, we reported the effectiveness of SRFA for hepatocellular carcinoma in 97 patients for bridging to liver transplantation. A complete histopathological response was achieved in 183 of 188 nodules (97.3%). Despite the use of SRFA alone, 50 of 52 nodules >3 cm (96.2%) showed complete response in explant histopathology.


Short- and long-term outcomes after SRFA


The short- and long-term outcomes after SRFA are comparable to liver surgery, even in non-resectable patients, in patients with multiple lesions, and in patients with lesions up to  >10 cm in diameter.


Due to the excellent results, stereotactic RFA has replaced surgical resection as the first-line treatment in Innsbruck in most liver tumour cases. Despite treatment of large lesions [5] and multiple lesions [6] simultaneously in one session, the complication rate after 2011 was 0.5% mortality and 6% major complications. More than half of these major complications could be treated in the same session by the interventional radiologist.


Since the implementation of SRFA including image fusion at our center in Innsbruck, the number of curative treatments in patients with primary and secondary liver tumours increased from 70 in 2001 to 280 in 2019 (+370%). The additional use of stereotaxy and image fusion enables the interventional radiologist to treat more patients more consistently, with curative intent, minimally invasively, and while sparing functional liver tissue.


Stereotactic thermal ablation is easy to learn, as the most difficult parts of the procedure (3D- planning) can be trained on virtual patient datasets. In conclusion, the additional efforts of 3D planning, stereotactic needle placement, and image fusion compared to conventional US- and CT- guided ablation approaches are justified by the excellent results that stereotactic thermal ablation yields.


Reto Bale


Medical University of Innsbruck, Innsbruck/AT


Prof. Reto Bale has been the Deputy Director of the Department of Radiology and the Division Chief of Interventional Oncology and Micro-insvasive Therapy at the University of Innsbruck since 2020. His main research areas include stereotactic thermal ablation (SRFA, SMWA, SIRE) 3D-navigation, and image fusion: CT- MR- PET- SPECT-ultrasound. He has collaborated in the development of numerous patents, including the VBH (Vogele- Bale- Hohner) Head holder, the Image-Guided Surgery System (Philips, EasyTaxis™), and the Targeting device (Medtronic, VERTEK™), among others. From 2014 to 2016, Prof. Bale headed the Austrian Society of Interventional Radiology (ÖGIR).



  1. Bale R, Freund M, Bodner G, et al. Precise Computerassisted Liver Tumor Puncture for Biopsy and Thermal Ablation. Radiology 2002;225:242.
  2. Laimer G, Schullian P, Jaschke N, et al. Minimal ablative margin (MAM) assessment with image fusion: an independent predictor for local tumor progression in hepatocellular carcinoma after stereotactic radiofrequency ablation. Eur Radiol 2020;30:2463-72
  3. Schullian P, Johnston E, Laimer G, et al. Thermal ablation of CT ‘invisible’ liver tumors using MRI fusion: a case control study. Int J Hyperthermia 2020;37:564-72.
  4. Bale R, Schullian P, Eberle G, et al. Stereotactic Radiofrequency Ablation of Hepatocellular Carcinoma: a Histopathological Study in Explanted Livers. Hepatology 2019;70:840-50.
  5. Schullian P, Johnston EW, Putzer D, et al. Safety and efficacy of stereotactic radiofrequency ablation for very large (≥8cm) primary and metastatic liver tumors. Sci Rep 2020;10:1618.
  6. Schullian P, Putzer D, Eberle G, et al. Simultaneous Stereotactic Radiofrequency Ablation of Multiple (≥ 4) Liver Tumors: Feasibility, Safety, and Efficacy. J Vasc Interv Radiol 2020;31:943-52.